One of the country's most notorious prisoners is under investigation after he assaulted a female nurse in jail, knocking her unconscious.

Jeffrey Dumbrell (35), who is currently serving a life sentence for murder, attacked the nurse and punched her in the face during a routine cell visit yesterday morning.

Dumbrell is alleged to have punched the victim so hard that she lost consciousness, and was immediately rushed to hospital where she received treatment for her injuries.

Several prison officers were also in the cell when the assault took place, and officials are investigating how the dangerous thug managed to launch the unprovoked attack on the nurse, despite warders being present.

The incident happened at approximately 11am yesterday at Wheatfield prison, west Dublin.

Dumbrell has racked up dozens of disciplinary reports since his incarceration and a source described him as an "extremely dangerous" individual.

"He is in trouble time and time again for incidents ranging from assault to damaging prison property.

"Dumbrell is well known, he is notorious for his behaviour and officials will have to investigate how he managed to attack the nurse, given his violent reputation," the source said.

Rampage

Only last month the dangerous inmate was involved in a violent rampage that lasted for 30 minutes and took three jail riot teams to contain.

The incident happened in a secure unit of Wheatfield prison just minutes after wife killer Eamon Lillis was released from the jail.

Dumbrell had asked to talk to a prison officer, but when the warder entered the unit, the thug threw a mug at him.

In total it took 15 officers from five different control and restraint teams to take command of the situation.

The prison officer was treated for minor cuts.

Inchicore brute Jeffrey and his older brother Warren Dumbrell (41) are serving life sentences for the murder of Christopher Cawley (33) on October 29, 2006.

The brothers' trial heard that Mr Cawley was fatally stabbed on the stairway of the flats complex where he lived at Tyrone Place, Inchicore.

Warren attacked him with a hurley and Jeffrey stabbed him six times.

He suffered three stab wounds to the back, one to the left hip and one to the back of each thigh.

Mr Cawley's wife Janette, son, and eldest daughter saw the attack. One of the Dumbrells said to the dead man's daughter as he walked away, "Your daddy's gone now", the court also heard.